In the realm of semiconductor fabrication, systems and methods for maximizing chip yield are critical to the success of a semiconductor manufacturing company. Higher yields allows companies to distribute the manufacturing costs over a greater quantity of products, thereby reducing the sales price or increasing the profit margin.
Optical, laser-based and SEM inspection tools are key pieces of equipment for yield maintenance and improvement. They are used to inspect wafers for defects at numerous points in the production process. Their data is used for three fundamental purposes: statistical process control (SPC), identification and quantification of the defects limiting yield for process improvement purposes, and yield modeling.
Inspection data is generally monitored using SPC since the number of defects is a good indicator of yields. A change in the distribution of defects can indicate a yield problem. Therefore, by monitoring inspection data, the yield problem may be detected in a timely manner. Despite the effectiveness of monitoring data, there is opportunity for improvement. Many types of defects may arise during manufacturing. These defects may be classified as either “killer” or “non-critical” defects. Killer defects cause a malfunction or failure of the semiconductor device, whereas non-critical defects do not substantially affect the performance of the semiconductor device. U.S. Pat. No. 6,047,083 describes one method of identifying defects in semiconductor products during their manufacture and for classifying such defects as “killer” or non-critical. However, once the defect has been identified as “killer”, the only solution is to adjust the manufacturing process to attempt to prevent future defects. It is not believed that the industry has addressed the repair of killer defects in order to salvage what otherwise would be defective products.
The majority of the yield loss for integrated circuits is due to killer defects that are a) of sub-micron size, b) the shorting together of elements of a single mask level (such as metal or gate-stack runners), or opens created at these same levels, and c) can be detected using in-line inspection tools such as an inspection SEM. This invention proposes a method of eliminating these defects in-line, thereby improving yield.